Reproducibility of Protected Brush Catheter Specimen Cultures in Critically Ill Patients with Suspected Nosocomial Pneumonia

Abstract

OBJECTIVE: To determine the reproducibility of two protected brush catheter (PBC) specimens obtained during the same bronchoscopy in critically ill patients with suspected ventilator associated pneumonia.DESIGN: Prospective, observational study.SETTING: Two university-affiliated multidisciplinary intensive care un its with a combined total of 50 beds.PATIENTS: A total of 75 (50 male. 25 female) patients with 84 episodes of suspected ventilator associated pneumonia were studied be tween January 1, 1991 and June 30, 1992. Age was 60.7±1.9 (mean ± SEM) years, and mean APACHE II score was 22.4±2.0. Twenty-four patients were admitted from various medical services, 19 from surgical services including the operating room, 16 with central nervous system disease and 16 following multiple trauma. Twenty patients were transferred directly to the intensive care unit from peripheral hospitals.INTERVENTIONS: All patients had lower respiratory tract secretions obtained for culture by both aspiration through the endotracheal n1be (tracheal aspirates) and flexible bronchoscopy, with separate samples obtained by two PBCs (PBC-A and PBC-8).MAIN RESULTS: The overall proportion of agreement between the results of t he two PBC specimens was 0.928, with a calculated kappa statistic (κ) = 0.853 (P<0.01 versus κ=0.4, 95% CL 0.692, 1.014) indicating excellent agreement between the two specimens. Both PBC specimens had significant (ie, more than 103colony-forming units/mL) growth (positive/positive) in 33 cases, nonsignificant growth in 45 cases (negative/negative) and discordant results in six (positive/negative, n=3 or negative/positive, n=3 ). There was a significant relationship (P<0.05) between the concurrent use of antibiotics and a negative PBC result. However, after exclusion of patients on antibiotics, the overall proportion of agreement between the two PBCs was 0.94 with κ=0.875 (P<0.01 versus κ=0.4, 95% CL 0.721, 1.029), which also indicates excellent agreement between the two tests.CONCLUSIONS: Although discordant results were observed in 7.2% cases, the overall reproducibility of the PBC results appears to be high. The significant relationship between concurrent antibiotic use and a negative PBC result is of concern clinically since many patients arc being treated with antibiotics al the time of bronchoscopy. Therefore, when the diagnosis of nosocomial pneumonia in critically ill patients is established, the PBC result should be considered only in association with all the other clinical data, particularly in patients receiving concurrent antibiotics.